It is known that contemporary optical fibers have relatively small optical cores often only a few micrometers in outer diameter, and an outer optical cladding having a diameter in an order of hundreds of micrometers in outer diameter, a refractive index difference between the optical cores and their corresponding optical claddings providing such contemporary optical fibers with light-guiding properties for conveying optical radiation bearing information therealong. Such light-guiding properties are employed widely within modern telecommunication systems. Such a relatively small outside diameter of the optical cores renders such fibers, especially monomode fibers having a core diameter of substantially 9 micrometers, potentially difficult to mutually align and thereby represents a problem in ensuring efficient coupling of optical energy therebetween. Although such coupling can be achieved by the use of precision zirconium ferrules to mutually precision abut fibers, practical problems are encountered in practice, especially regarding particulate contamination and condensation.
Various approaches have been proposed for rendering optical fibers easier to mutually couple. For example, in a published international PCT patent application no. PCT/US02/23700 (WO 03/010564), there is described an expanded beam connector system illustrated in cross-sectional view in FIG. 1. The system indicated generally by 10 comprises a precision alignment tubular sleeve 20 having first and second ends 30a, 30b. First and second ferrules 40a, 40b are accommodated at the first and second ends 30a, 30b respectively of the sleeve 20 and extend into the sleeve 20 as illustrated. The first and second ferrules 40a, 40b include first and second collimating lenses 50a, 50b therein respectively. Moreover, a free-space region 60 between the first and second lenses 50a, 50b is permitted to remain substantially at a central portion of the sleeve 20. At faces 70a, 70b of the lenses 50a, 50b remote from the free-space region 60, the sleeve 20 provides support for first and second optical fibers 80a, 80b to abut to the first and second lenses 50a, 50b respectively, these fibers 80a, 80b each including a central optical core 82a, 82b and corresponding optical cladding 84a, 84b therearound. In operation, optical radiation guided substantially along the core 82a of the first fiber 80a propagates through the first lens 50a wherein the optical radiation is formed into a substantially collimated beam 90 whose diameter is considerably greater than that of the core 82a of the first fiber 50a. The collimated beam 90 propagates through the aforementioned free-space region 60 to be received by the second lens 50b which is operable to focus the received radiation to a focal point whereat the core 82b of the second fiber 80b is positioned. The radiation received at the core 82b of the second fiber 80b continues by propagating along the second fiber 80b. The aforesaid expanded beam connector system 10 is capable of coupling optical radiation from one type of optical fiber to another. Moreover, the connector system 10 is adapted for coping with relatively high-power optical signals. A benefit provided by the beam connector system 10 is that the optical radiation propagating in the free-space region 60 is conveyed by way of a beam of relatively large outer diameter, for example several hundred micrometers in outer diameter, rendering adjustment of the first and second fibers 80a, 80b to be relatively less critical for ensuring efficient coupling of the radiation from the first fiber 80a to the second fiber 80b and vice versa. The first ferrule 40a provides for mutual location of both the first fiber 80a and its corresponding first collimating lens 50a. Similarly, the second ferrule 40b provides for mutual location of both the second fiber 80b and its corresponding second collimating lens 50b. The precision alignment sleeve 20 provides for relative mutual alignment of the first and second ferrules 40a, 40b. In use, the collimated beam 90 renders mutual alignment of the first and second ferrules 40a, 40b less critical. The fibers 80a, 80b and their associated lenses 50a, 50b together with their ferrules 40a, 40b are fixed together and are not susceptible to being disassembled after initial manufacture. However, the ferrules 40a, 40b are capable of being mated and unmated from the tube 20 in use.
A further example of a contemporary approach to coupling optical radiation from a first optical fiber to a second optical fiber in an optical connection is described in a published United Kingdom patent no. GB 2, 145, 534. The optical connection includes first and second spherical lenses abutted to corresponding tapered location faces in first and second inner members. In the optical connection, the spherical lenses are retained in mutually spaced-apart disposition with a radiation propagation region provided therebetween. The first and second members also include tapered cavities for receiving ends of first and second optical fibers. The first and second members abut by way of tapered faces onto first and second corresponding tapered members. Moreover, the first and second tapered members are housed within a tubular member. In operation, the tubular member ensures that the first and second inner members are correctly positioned so that their lenses and fibers are corrected spaced and mutually in alignment. The optical connection functions in substantially a similar manner to the aforementioned expanded beam connector system. However, the optical connection employs many precision component parts and only caters for adjustment of a distance between the spherical lenses, namely an axial length of the radiation propagation region provided between the spherical lenses. Precise lateral alignment of the optical fibers to their corresponding lenses is provided inherently by use of the tapered cavities and the tapered faces of the first and second tapered members and corresponding tapered faces of the first and second inner members. The optical connection is thereby potentially costly to manufacture on account of a relatively large number of precision parts being required to be precision manufactured and thereafter mutually assembled. Moreover, the optical connection is adapted for coupling multimode fibers together whose central optical cores have a diameter in the order of 50 micrometers. The optical connection is unsuitable for coupling monomode fibers together, such fibers have an optical core diameter in the order of 9 micrometers, on account of excessive precision to which component parts of the optical connection would have to be manufactured.
Thus, the aforementioned expanded beam connector system does not allow for decoupling of its optical fibers from their respective lenses in use, and the optical connection is complex and potentially costly to manufacture on account of precision components being required for its manufacture.